Gallium-nitride based light emitting diode light emitting layer structure

ABSTRACT

A number of light-emitting layer structures for the GaN-based LEDs that can increase the lighting efficiency of the GaN-based LEDs on one hand and facilitate the growth of epitaxial layer with better quality on the other hand are provided. The light-emitting layer structure provided is located between the n-type GaN contact layer and the p-type GaN contact layer. Sequentially stacked on top of the n-type GaN contact layer in the following order, the light-emitting layer contains a lower barrier layer, at least one intermediate layer, and an upper barrier layer. That is, the light-emitting layer contains at least one intermediate layer interposed between the upper and lower barrier layers. When there are multiple intermediate layers inside the light-emitting layer, there is an intermediate barrier layer interposed between every two immediately adjacent intermediate layers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the gallium-nitride (GaN) based lightemitting diode (LED), and in particular to the structure of thelight-emitting layer of the GaN-based LED.

2. The Prior Arts

LEDs have long been widely used as indicators or light sources invarious electronic consumer devices due to their features including lowpower consumption, low heat dissipation, and long operation life. Inrecent years, researches have been focused on the development of LEDswith various colors and LEDs with high luminance. Among theseresearches, highly efficient and illuminant blue-light LEDs that can beput to practical use receive the most attention. In October 1995, NichiaCorporation, Japan, announced the successful production of highlyilluminant blue-light LEDs based on the indium-gallium-nitride (InGaN)material. This breakthrough has led the world's optoelectronic industryto invest tremendous capitals and resources in the gallium-nitride (GaN)based, such as GaN, aluminum-gallium-nitride (AlGaN),indium-gallium-nitride (InGaN), etc., LEDs.

FIG. 1 is a schematic diagram showing the structure of a GaN-based LEDaccording to prior arts. As shown in FIG. 1, the conventional structureof a GaN-based LED contains a substrate 10 made of sapphire. Then, onone side of the sapphire substrate 10, the GaN-based LED furthercontains a n-type GaN contact layer 11, a InGaN light-emitting layer 12,and a p-type GaN contact layer 13, sequentially stacked from bottom totop in this order. In addition, there are a positive electrode 14 and anegative electrode 15 stacked upon the p-type GaN contact layer 13 andthe n-type GaN contact layer 11 respectively. Within this conventionalGaN-based LED structure, the light-emitting layer 12 usually has amulti-quantum well (MQW) structure made of In_(x)Ga_(1-x)N (0≦x≦1). Theelectrons and holes are joined with each other within theIn_(x)Ga_(1-x)N (0≦x≦1) potential well and photons are thereby released.Please note that the epitaxial growth of the In_(x)Ga_(1-x)N (0≦x≦1)requires a very high temperature to obtain epitaxial layer with betterquality. On the other hand, to increase the possibility of forming theelectron-hold pairs and thereby the lighting efficiency, the growingtemperature of the In_(x)Ga_(1-x)N (0≦x≦1) cannot be higher than 850° C.so that multiple localized states can be formed from the characteristicsof the In_(x)Ga_(1-x)N (0≦x≦1) such as indium segregation and phaseseparation. This is a dilemma requiring an appropriate solution.

SUMMARY OF THE INVENTION

To overcome the foregoing disadvantages, the present invention providesa number of light-emitting layer structures for the GaN-based LEDs thatcan increase the lighting efficiency of the GaN-based LEDs on one handand facilitate the growth of epitaxial layer with better quality on theother hand.

The light-emitting layer structure provided by the present invention islocated between the n-type GaN contact layer and the p-type GaN contactlayer. Sequentially stacked on top of the n-type GaN contact layer inthe following order, the light-emitting layer contains a lower barrierlayer, at least one intermediate layer, and an upper barrier layer. Thatis, the light-emitting layer contains at least one intermediate layerinterposed between the upper and lower barrier layers. When there aremultiple intermediate layers inside the light-emitting layer, there isan intermediate barrier layer interposed between every two immediatelyadjacent intermediate layers.

The upper and lower barrier layers have higher band gaps than that ofthe intermediate layer so that the electrons and the holes have a higherpossibility joining with each other within the intermediate layer, whichin turn increase the lighting efficiency of the GaN-based LED. Thebarrier layers have a thickness between 5 Å and 300 Å, and a growingtemperature between 400° C. and 1000° C.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become better understood from a careful readingof a detailed description provided herein below with appropriatereference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the structure of a conventionalGaN-based LED.

FIGS. 2(a), 2(b), and 2(c) are schematic diagrams showing the GaN-basedLED structures according to a first embodiment of the present invention.

FIGS. 3(a), 3(b), and 3(c) are schematic diagrams showing the GaN-basedLED structures according to a second embodiment of the presentinvention.

FIGS. 4(a) and 4(b) are schematic diagrams showing the GaN-based LEDstructures according to a third embodiment of the present invention.

FIGS. 5(a) and 5(b) are schematic diagrams showing the GaN-based LEDstructures according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 2(a), 2(b), and 2(c) are schematic diagrams showing the GaN-basedLED structures according to a first embodiment of the present invention.As shown in FIGS. 2(a), 2(b), and 2(c), the GaN-based LED structures usesapphire as the substrate 20. Then, sequentially from bottom to top onthe sapphire substrate 20, the GaN-based LED structures contain a n-typeGaN contact layer 21, a lower barrier layer 22 made of un-dopedaluminum-gallium-indium-nitride (Al_(1-x-y)Ga_(x)In_(y)N, 0≦x,y≦1,x+y≦1), at least an intermediate layer 23, an upper barrier layer 24made of un-doped Al_(1-p-q)Ga_(p)In_(q)N (0≦p,q≦1, p+q≦1), and a p-typeGaN contact layer 25. The GaN-based LED structures further contain apositive electrode 26 and a negative electrode 27 on top of the p-typeGaN contact layer 25 and the n-type GaN contact layer 21 respectively.

As shown in FIG. 2(a), the intermediate layer 23 further contains, frombottom to top, an ultra-thin quantum-dot layer 231 made ofindium-nitride (InN) and a quantum-well layer 232 made of un-dopedAl_(1-m-n)Ga_(m)In_(n)N (0≦m,n≦1, m+n≦1).

As shown in FIG. 2(b), the intermediate layer 23 can further contain anoptional InN ultra-thin quantum-dot layer 231′ on top of the un-dopedAl_(1-m-n)Ga_(m)In_(n)N (0≦m,n≦1, m+n≦1) quantum-well layer 232.

As shown in FIG. 2(c), when there are multiple intermediate layers,every two immediately adjacent intermediate layers 23 and 23′ have anintermediate barrier layer 28 made of un-doped Al_(1-i-j)Ga_(i)In_(j)N(0≦i,j≦1, i+j≦1) interposed therebetween.

The upper, intermediate, and lower barrier layers 24, 28, and 22 allhave a thickness between 5 Å and 300 Å, and a growing temperaturebetween 400° C. and 1000° C. The ultra-thin quantum-dot layers 231 and231′ have a thickness between 2 Å and 30 Å, and a growing temperaturebetween 400° C. and 1000° C. The quantum-well layer 232 has a thicknessbetween 5 Å and 100 Å. Even though the quantum-well layer and thebarrier layers are all made of aluminum-gallium-indium-nitrides, theircompositions are not required to be identical. That is, the (x, y), (p,q), (m, n), (i, j) parameters in the foregoing molecular formulas arenot necessarily the same.

FIGS. 3(a), 3(b), and 3(c) are schematic diagrams showing the GaN-basedLED structures according to a second embodiment of the presentinvention. The second embodiment and the foregoing first embodiment ofthe present invention actually have identical structures. The differencelies in the materials used for the respective intermediate layers. Asshown in FIG. 3(a), the intermediate layer 33 further contains, frombottom to top, an ultra-thin layer 331 made of InN and quantum-welllayer 332 made of un-doped Al_(1-m-n)Ga_(m)In_(n)N (0≦m,n≦1, m+n≦1).

As shown in FIG. 3(b), the intermediate layer 33 can further containanother optional InN ultra-thin layer 331′ on top of the un-dopedAl_(1-m-n)Ga_(m)In_(n)N (0≦m,n≦1, m+n≦1) quantum-well layer 332.

As shown in FIG. 3(c), when there are multiple intermediate layers,every two immediately adjacent intermediate layers 33 and 33′ must havean intermediate barrier layer 38 made of un-dopedAl_(1-i-j)Ga_(i)In_(j)N (0≦i,j≦1, i+j≦1) interposed therebetween.

The upper, intermediate, and lower barrier layers 34, 38, and 32 allhave a thickness between 5 Å and 300 Å, and a growing temperaturebetween 400° C. and 1000° C. The ultra-thin layers 331 and 331′ have athickness between 2 Å and 10 Å, and a growing temperature between 400°C. and 1000° C. The quantum-well layer 332 has a thickness between 5 Åand 100 Å. Even though the quantum-well layer and the barrier layers areall made of aluminum-gallium-indium-nitrides, their compositions are notrequired to be identical. That is, the (x, y), (p, q), (m, n), (i, j)parameters in the foregoing molecular formulas are not necessarily thesame.

FIGS. 4(a) and 4(b) are schematic diagrams showing the GaN-based LEDstructures according to a third embodiment of the present invention. Thethird embodiment and the previous two embodiments of the presentinvention actually have identical structures. The difference lies in thematerials used for the respective intermediate layers. As shown in FIG.4(a), the intermediate layer 43 is a supper lattice well layer furthercontaining at least an InN ultra-thin monolayer 431 and a GaN ultra-thinmonolayer 432. Within the intermediate layer 43, the monolayers aresequentially stacked and interleaved with each other. For one example,from the lower barrier layer 42 up, there are InN ultra-thin monolayer431, GaN ultra-thin monolayer 432, then another InN ultra-thin monolayer431′, and then another GaN ultra-thin monolayer 432′, and so on. Foranother example, from the lower barrier layer 42 up, there are GaNultra-thin monolayer 432, InN ultra-thin monolayer 431, then another GaNultra-thin monolayer 432′, and then another InN ultra-thin monolayer431′, and so on. The monolayers all have a thickness between 2 Å and 20Å, and a growing temperature between 400° C. and 1000° C. Within theintermediate layer 43, there are at least one InN ultra-thin monolayer431 and one GaN ultra-thin monolayer 432, making the total number ofmonolayers at least two. On the other hand, within the intermediatelayer 43, there are at most five InN ultra-thin monolayers 431 and fiveGaN ultra-thin monolayers 432, making the total number of monolayers atmost ten.

As shown in FIG. 4(b), when there are multiple intermediate layers,every two immediately adjacent intermediate layers 43 and 43′ must havean intermediate barrier layer 48 made of un-dopedAl_(1-i-j)Ga_(i)In_(j)N (0≦i,j≦1, i+j≦1) interposed therebetween.

The upper, intermediate, and lower barrier layers 44, 48, and 42 allhave a thickness between 5 Å and 300 Å, and a growing temperaturebetween 400° C. and 1000° C. Even though the barrier layers are all madeof aluminum-gallium-indium-nitrides, their compositions are not requiredto be identical. That is, the (x, y), (p, q), (i, j) parameters in theforegoing molecular formulas are not necessarily the same.

FIGS. 5(a) and 5(b) are schematic diagrams showing the GaN-based LEDstructures according to the fourth embodiment of the present invention.The fourth embodiment and the third embodiment of the present inventionactually have identical structures. The difference lies in the materialsused for the upper, intermediate, and lower barrier layers. As shown inFIGS. 5(a) and 5(b), each barrier layer has a structure identical tothat of the intermediate layer 43. Specifically, each barrier layer is asupper lattice barrier layer further containing at least an In-doped,AlN ultra-thin monolayer 531 and an In-doped, GaN ultra-thin monolayer532. Within each the barrier layer, the monolayers are sequentiallystacked and interleaved with each other, similar to the intermediatelayer 43. The monolayers all have a thickness between 2 Å and 20 Å, anda growing temperature between 400° C. and 1000° C. Within each barrierlayer, there are at least one AlN ultra-thin monolayer 531 and one GaNultra-thin monolayer 532, making the total number of monolayers at leasttwo. On the other hand, within each barrier layer, there are at mostfive AlN ultra-thin monolayer 531 and five GaN ultra-thin monolayer 532,making the total number of monolayers at most ten. The upper,intermediate, and lower barrier layers 54, 58, and 52 may containdifferent numbers of monolayers respectively. However, the barrierlayers all have a thickness between 5 Å and 300 Å, and a growingtemperature between 400° C. and 1000C.

Although the present invention has been described with reference to thepreferred embodiments, it will be understood that the invention is notlimited to the details described thereof. Various substitutions andmodifications have been suggested in the foregoing description, andothers will occur to those of ordinary skill in the art. Therefore, allsuch substitutions and modifications are intended to be embraced withinthe scope of the invention as defined in the appended claims.

1. A light-emitting layer structure of a gallium-nitride (GaN) basedlight emitting diode (LED), wherein said LED comprises a sapphiresubstrate and comprises, on one side of said substrate from bottom totop, a n-type GaN contact layer, a light-emitting layer covering a partof an upper surface of said n-type GaN contact layer; a p-type GaNcontact layer covering said light-emitting layer, a positive electrodecovering said p-type GaN contact layer, and a negative electrodecovering another part of said upper surface of said n-type GaN contactlayer not covered by said light-emitting layer, wherein saidlight-emitting layer, sequentially from bottom to top, comprises: alower barrier layer made of un-doped aluminum-gallium-indium-nitride(Al_(1-x-y)Ga_(x)In_(y)N, 0≦x,y≦1, x+y≦1); at least an intermediatelayer, wherein, when there are more than one said intermediate layer,said intermediate layers stack sequentially and an intermediate barrierlayer made of un-doped Al_(1-i-j)Ga_(i)In_(j)N (0≦i,j≦1, i+j≦1) isinterposed between every two immediately adjacent said intermediatelayers; and an upper barrier layer made of un-dopedAl_(1-p-q)Ga_(p)In_(q)N (0≦p,q≦1, p+q≦1).
 2. The light-emitting layerstructure of a GaN-based LED according to claim 1, wherein saidintermediate layer comprises, from bottom to top, a first ultra-thinquantum-dot layer made of indium-nitride (InN) and a quantum-well layermade of un-doped Al_(1-m-n)Ga_(m)In_(n)N (0≦m,n≦1, m+n≦1).
 3. Thelight-emitting layer structure of a GaN-based LED according to claim 2,wherein said intermediate layer further comprises a second ultra-thinquantum-dot layer made of InN on top of said quantum-well layer.
 4. Thelight-emitting layer structure of a GaN-based LED according to claim 2,wherein said upper, intermediate, and lower barrier layers all have athickness between 5 Å and 300 Å, said first ultra-thin quantum-dot layerhas a thickness between 2 Å and 30 Å, and said quantum-well layer has athickness between 5 Å and 100 Å.
 5. The light-emitting layer structureof a GaN-based LED according to claim 3, wherein said upper,intermediate, and lower barrier layers all have a thickness between 5 Åand 300 Å, said first and said second ultra-thin quantum-dot layers allhave a thickness between 2 Å and 30 Å, and said quantum-well layer has athickness between 5 Å and 100 Å.
 6. The light-emitting layer structureof a GaN-based LED according to claim 1, wherein said intermediate layercomprises, from bottom to top, a first ultra-thin layer made of InN anda quantum-well layer made of un-doped Al_(1-m-n)Ga_(m)In_(n)N (0≦m,n≦1,m+n≦1).
 7. The light-emitting layer structure of a GaN-based LEDaccording to claim 6, wherein said intermediate layer further comprisesa second ultra-thin layer made of InN on top of said quantum-well layer.8. The light-emitting layer structure of a GaN-based LED according toclaim 6, wherein said upper, intermediate, and lower barrier layers allhave a thickness between 5 Å and 300 Å, said first ultra-thin layer hasa thickness between 2 Å and 10 Å, and said quantum-well layer has athickness between 5 Å and 100 Å.
 9. The light-emitting layer structureof a GaN-based LED according to claim 7, wherein said upper,intermediate, and lower barrier layers all have a thickness between 5 Åand 300 Å, said first and said second ultra-thin layers all have athickness between 2 Å and 10 Å, and said quantum-well layer has athickness between 5 Å and 100 Å.
 10. The light-emitting layer structureof a GaN-based LED according to claim 1, wherein said intermediate layeris a super lattice well layer comprising at least a first ultra-thinmonolayer made of InN and at least a second ultra-thin monolayer made ofGaN, sequentially stacked and interleaved with each other.
 11. Thelight-emitting layer structure of a GaN-based LED according to claim 10,wherein said first ultra-thin monolayers and said second ultra-thinmonolayers have identical number of layers, no more than five layersrespectively, and a thickness between 2 Å and 20 Å for each individuallayer.
 12. The light-emitting layer structure of a GaN-based LEDaccording to claim 10, wherein said upper, intermediate, and lowerbarrier layers all have a thickness between 5 Å and 300 Å.
 13. Alight-emitting layer structure of a GaN-based LED, wherein said LEDcomprises a sapphire substrate and comprises, on one side of saidsubstrate from bottom to top, a n-type GaN contact layer, alight-emitting layer covering a part of an upper surface of said n-typeGaN contact layer, a p-type GaN contact layer covering saidlight-emitting layer, a positive electrode covering said p-type GaNcontact layer, and a negative electrode covering another part of saidupper surface of said n-type GaN contact layer not covered by saidlight-emitting layer, wherein said light-emitting layer, sequentiallyfrom bottom to top, comprises: a lower barrier layer, wherein said lowerbarrier layer is a super lattice barrier layer comprising at least afifth ultra-thin monolayer made of AlN and at least a sixth ultra-thinmonolayer made of GaN, sequentially stacked and interleaved with eachother; at least an intermediate layer, wherein, when there are more thanone said intermediate layer, said intermediate layers stack sequentiallyand an intermediate barrier layer, being a super lattice barrier layercomprising at least a seventh ultra-thin monolayer made of In-doped AlNand at least a eighth ultra-thin monolayer made of In-doped GaNsequentially stacked and interleaved with each other, is interposedbetween every two immediately adjacent said intermediate layers; and anupper barrier layer, wherein said upper barrier layer is a super latticebarrier layer comprising at least a ninth ultra-thin monolayer made ofAlN and at least a tenth ultra-thin monolayer made of GaN, sequentiallystacked and interleaved with each other.
 14. The light-emitting layerstructure of a GaN-based LED according to claim 13, wherein saidintermediate layer is a super lattice well layer comprising at least athird ultra-thin monolayer made of InN and at least a fourth ultra-thinmonolayer made of GaN, sequentially stacked and interleaved with eachother.
 15. The light-emitting layer structure of a GaN-based LEDaccording to claim 13, wherein said upper, intermediate, and lowerbarrier layers all have a thickness between 5 Å and 300 Å.
 16. Thelight-emitting layer structure of a GaN-based LED according to claim 14,wherein said third ultra-thin monolayers and said fourth ultra-thinmonolayers have identical number of layers, no more than five layersrespectively, and a thickness between 2 Å and 20 Å for each individuallayer.
 17. The light-emitting layer structure of a GaN-based LEDaccording to claim 13, wherein said fifth ultra-thin monolayers and saidsixth ultra-thin monolayers have identical number of layers, no morethan five layers respectively, and a thickness between 2 Å and 20 Å foreach individual layer.
 18. The light-emitting layer structure of aGaN-based LED according to claim 13, wherein said seventh ultra-thinmonolayers and said eighth ultra-thin monolayers have identical numberof layers, no more than five layers respectively, and a thicknessbetween 2 Å and 20 Å for each individual layer.
 19. The light-emittinglayer structure of a GaN-based LED according to claim 13, wherein saidninth ultra-thin monolayers and said tenth ultra-thin monolayers haveidentical number of layers, no more than five layers respectively, and athickness between 2 Å and 20 Å for each individual layer.